Fluid bed dryer

Theory Fluid bed dryer

Fluid bed dryer: If gas is allowed to flow upward through a bed of solid particles at a velocity greater than the setting velocity of the particles, the particles are partially suspended in the gas stream. The resultant mixture of solids and gas behaves like a liquid and the solids are said to be fluidized. Each individual solid particle is surrounded by the drying gas with the result that drying takes place in a much shorter period.

Fluid bed dryer

Two types of fluidized bed dryers are used

  1. Vertical fluidized bed dryers.
  2. Horizontal fluidized bed dryers.

A typical vertical fluidized bed dryer is shown in fig. The fluidizing air stream is induced by a fan which is mounted in the upper part of the dryer. The air is heated to the required temperature in air heaters and passed through the wet material contained in a drying chamber fitted with a wire mesh support at the bottom. The airflow rate is adjusted by means of re-circulation control and fabric filter bags are provided to prevent the passage of fine particles. Horizontal vibrating conveyer fluidized bed dryers are used for the continuous drying of a large volume of material.

Advantages of Fluid bed dryer

  1. It gives a high drying rate. The fluidized bed dryer method is 15 times faster than the routine method of a tray dryer.
  2. The method is suitable for drying thermolabile materials because heating time is minimized.
  3. In a fluidized bed dryer, drying takes place from individual particles and not from the entire bed. As such most of the drying takes place at a constant rate and there is less danger of overheating.
  4. The temperature inside the fluidized bed dryer can be controlled moreover the temperature is uniform.
  5. The free movement of individual particles prevents the risk of soluble materials migrating which may occur in static beds.
  6. The fluidized bed dryer has a high output and occupies a small floor space.
  7. It can be used for drying any powdered material but it is mostly used for drying of granules meant for the manufacture of tablets.

Disadvantages of Fluid bed dryer

  1. The turbulence produced when hot air is passed through the material may cause attrition of some material, which leads to the production of fines.
  2. The vigorous movement of solid particles in hot air can lead to the generation of an electric charge. Hence suitable precautions must be taken in this regard.

Applications of Drying

  1. In the pharmaceutical industry, it is used as a unit process in the manufacture of granules which can be dispensed in bulk or converted into tablets or capsules.
  2. Drying can also be used to reduce the bulk and weight of the material, thereby lowering the cost of transportation and storage.
  3. It helps in the preservation of crude drugs of plant and mould growth, which occurs due to the presence of moisture.
  4. It helps in the side reduction of crude drugs. The presence of moisture in the crude drug does not allow it to get powdered easily.
  5. Drying is also used in the processing of materials e.g. the preparation of dried aluminum hydroxide, the spray drying of lactose, and the preparation of solid extracts.

Also read: Principle construction, and working of ball mill

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